390 Naohide Yatsu. 



of cell division bj means of inorganic objects. The last method is 

 a rather dangerous one. Only with the greatest cantion should one 

 apply the simulacra thus obtained to our problem. Another line 

 of attack may be offered as a fourth method. This comprises cutting 

 and compressing experiments performed on living cells at different 

 periods of division. How important this method is, may be il- 

 lustrated by Wilson's experiment on the egg of Dentalium. The 

 formation of the polar lobe is naturally intei"}3reted as due to the 

 action of the two centres in the egg (cf. Bomievie, '03, p. 101). 

 Wilson ('04) found out by a simple cutting experiment that the 

 polar lobe is formed in enucleated egg fragments free from asters 

 (Carazzi, '05, p. 15). Simple as it is, by this method one can test 

 the validity of interpretations hitherto proposed. Although this 

 has been singularly neglected, yet I think the mechanism of cell 

 division will in future be studied most advantageously along this 

 line. 



What actually happens during cell division is the rounding-up of 

 the cytoplasm around the two centres (Rhumbler, '97, p. Y05, Mor- 

 gan, '99, p. 521, Teichmann, '03, p. 316). This is undoubtedly the 

 resultant of several factors. Of these the following may be men- 

 tioned : The surface tension is usually disturbed at the farthest point 

 from the centre, causing pseudopodia or irregular outlines (Erlanger, 

 '97c, p. 344, Rhumbler, '01, p. 63, 65 and 69, Conklin, '02, p. 94, 

 Boveri, '03, pp. 3 and 5, Jolly, '04, pp. 504 and 505, e. g., Fig. 11 

 70h 38, Fig. 10 3h 40, 7h 48). As Boveri thinks, this phenomenon 

 seems to be very important for the explanation of the formation of 

 the constriction. By this factor alone the egg should divide by the vege- 

 tative furrow. But in reality the animal furrow is the first to 

 appear and in some cases the vegetative furrow is very insignificant. 

 This, as often has been pointed out, is due to the position of the 

 nucleus. The nuclear fluid after the dissolution of its walls takes 

 the form of Biitschli's space (Bonnevie, '06, Kornerhilllc, ]). 286.)"^ 



°°Conklin thinks that the nuclear fluid escapes from the poles at the fading 

 of the nuclear nieiubrano. This is true for the formations of the rays which 

 give rise to the spindle. Hut it cannot be doubted that the greater part of tL^i 

 nuclear fluid remains m situ and later forms Biitschli's space as Rhumbler 

 maintains. 



